You can use both the free and the premium version of Yousician with your students.
The free version is a great risk-free way to start with Yousician, and see how it works for you and your students. Their practice time will be limited, but during the daily free lesson they'll receive feedback on accuracy and timing, earn stars, advance through missions, etc.
The big advantage of the premium version is that practice time is unlimited. So, students who pay for Yousician can practice as much as they like, and spend the time they need to improve quickly, refine their skills, and build mastery. As you know, learning an instrument requires countless hours of effort and attention, and Yousician premium helps make the journey engaging, motivating and rewarding.
In our experience, students (and the parents of younger students) understand exactly why teachers use Yousician as part of their curriculum. If a teacher recommends it as learning material instead of a book, students are usually happy to buy it without hesitation.